322 REACTION OP THE INTERIOR OF THE EAIITII 



connection, which all the volcanoes of Pasto and Quito 

 bear to the volcanic hearth of the equatorial Cordilleras, 

 embracing an area of very many hundred square miles. 

 Were these pumice-stones the centre and interior of a 

 special crater of elevation, whose outer encircling ridge 

 has been destroyed in the many revolutions which the 

 earth's surface has undergone in thee regions ? or were 

 they deposited horizontally, in apparent tranquillity, over 

 fissures at the time of the first crumpling or folding of 

 the earth's crust ? For still greater difficulties attach 

 to the supposition of their having been deposited as 

 sediment from flows of water, as is often seen in volcanic 

 masses of tufa, mixed with remains of plants and 

 shells. 



Similar questions are suggested by the great masses 

 of pumice, at a distance from any volcanic eleva- 

 tion, which I found in the Cordillera of Pasto, between 

 Mamendoy and the Cerro del Pulpito, near the Eio 

 Mayo, 36 geographical miles north of the active vol- 

 cano of Pasto. Leopold von Buch has also called at- 

 tention to a similarly isolated outbreak of pumice, 

 described by Meyen, in Chili, east of Valparaiso, near 

 the village of Tollo, where it forms a hill about 300 feet 

 high. The volcano of Maypo, which in its upheaval 

 lifted up Jurassic strata, is two entire days' journeys from 

 this outbreak of pumice. ( 459 ) The Prussian Envoy at 

 Washington, Friedrich von Grerolt, to whom we owe 

 the first coloured geological map of Mexico, mentions 

 pumice-stone being obtained from beneath the surface 

 of the ground for building purposes, near Huichapa, 32 

 geographical miles south-east of Queretaro, at a distance 

 from any volcano. ( 46 ) The geological investigator of 



